From the distribution of 14C in hydroxybutyrate extracted from the urine of ketotic alloxan-induced diabetic rats given specifically 14C-labeled fatty acids, the extent of formation of acetoacetyl-CoA directly from the terminal four carbons of the fatty acids will be estimated. An estimate will also be made of how much acetoacetyl-CoA is directly deacylated rather than being deacylated via the HMGCoA pathway. Evidence as to whether or not L-hydroxybutyrate is formed will also be sought. The study should provide a quantitative measure in the intact animal of the contributions of various reactions to ketone body formation, reactions whose regulation may be of significance in the development of ketosis.